Valence band orbital polarization in III-V ferromagnetic semiconductors

Abstract

The element-specific technique of x-ray magnetic circular dichroism (XMCD) is used to directly determine the magnitude and character of the valence band orbital magnetic moments in (III,Mn)As ferromagnetic semiconductors. A distinct dichroism is observed at the As K absorption edge, yielding an As 4p orbital magnetic moment of around -0.1 Bohr magnetons per valence band hole. This is strongly influenced by strain, indicating its crucial influence on the magnetic anisotropy. The dichroism at the Ga K edge is much weaker. The K edge XMCD signals for Mn and As both have positive sign, which indicates the important contribution of Mn 4p states to the Mn K edge spectra.Comment: 5 pages, 2 figure

Itinerant Ferromagnetism in the As4pConduction Band ofBa0.6K0.4Mn

“…The lines correspond to fits to the peak using a Lorentzian lineshape. These data provide evidence of the FM orbital polarization of the As 4p conduction band and are similar in appearance to previous As K edge XMCD spectra in, for example, the Ga 1−x Mn x As FM semiconductor [29,30].…”

“…We note that our TFY data may be strongly distorted by self-absorption effects [31], and we therefore use our TEY data as a basis for the upper estimate of 0.02 µ B for the size of any FM ordered Mn moment present. For measurements at the Mn K edge, comparison to similar data taken for (In,Ga,Mn)As [29] show that our experiments would detect a Mn moment ≥ 0.15 µ B . This indicates that measurements at the Mn L 2 and L 3 edges are an order of magnitude more sensitive to the size of the moment than measurements at the Mn K edge.…”

“…In these cases, an XMCD signal was also found at the L 2 and L 3 edges of the transition metals, and it was determined that the measured K edge signals were due to polarization of the 4p orbital moments by the 3d moments of neighboring transition metal sites [29,30,36]. As we have shown, this is not the case for Ba 0.6 K 0.4 Mn 2 As 2 since no distinct peaks in the XMCD signal were observed at the Mn edges.…”

Element specific magnetic properties of Gd-doped GaN: Very small polarization of Ga and paramagnetism of Gd

“…From the SQUID measurements a overall magnetic polarization of 1.1 · 10 −3 µ B has been inferred inside the "spheres of influence" [2]. The XMCD results can be compared to recent experimental data recorded at the Ga K-edge of (InGaMn)As [9]. Here a Ga 4p orbital moment of 8(4) · 10 −5 µ B has been correlated with a maximum XMCD intensity of 0.05%.…”

“…1(b) one can roughly estimate a magnetic moment of the order of at most 10 −5 µ B as upper bound, since the integral of the XMCD in our case is close to zero, whereas in Ref. [9] the spectral shape indicates only one positive feature, i. e., a larger integral for the same amplitude. This is between one and two orders of magnitude smaller than what is expected from the SQUID measurements.…”